Synchrotron-based X-ray techniques are particularly useful for probing the effects of electrode preparation process and the fuel cell operating conditions on the degradation of high surface area carbon-supported platinum and platinum-alloy nano-particle electrocatalysts. These studies have mainly utilized ex situ microscopy techniques or in situ evaluation of electrochemically-active surface area and electrocatalytic activity.  In this paper, we report on studies using X-ray absorption spectroscopy (XAS), small angle X-ray scattering (SAXS) and ultra small angle X-ray scattering (USAXS) to study the key mechanistic steps in the degradation of Pt and Pt alloy nano-particle electrocatalysts in aqueous and MEA environments, and to derive the size and geometry of the components of the electrode. The XAS and ASAXS techniques allow correlation of the loss of electrochemically-active surface area and ORR activity with particle growth (ASAXS) processes and with Pt loss (XAFS edge step analysis) and/or alloying element loss.  In addition, because these are in situ/in operando techniques, these processes can be related to the extent of catalyst component oxidation (XANES analysis) as a function of cell operating conditions.  Information from combined USAXS-pinSAXS technique is correlated with the effects of the electrode preparation process on the final electrode structure, towards optimization of the performance of the state-of-the-art Pt alloy/C based MEAs.

X-ray scattering and absorption studies of polymer electrolyte fuel cell cathode electrocatalysts

248th National Meeting (2014)

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